Counter-torque wrenches are used to help prevent undesired forces from being transmitted to spinal bone screws, thereby minimizing forces that may otherwise result in the screw breaking through bone as tightening torques are applied. Known counter-torque wrenches incorporate two straight slots configured to receive a rod and can pivot on the rod or be otherwise skewed relative to the rod when engaged with the rod. That is, the body of the wrench may not always be perpendicular to the axis of the rod. When a standard counter-torque wrench engages the rod and the screw body, there is no geometry for the wrench body to key into to promote a perpendicular orientation between the screw body and the rod. A standard counter-torque wrench can pivot on the rod or otherwise be skewed relative to the rod when it engages both the screw body and the rod. If the screw body is forced to stay in this skewed orientation, the set screw's ability to clamp the rod can be negatively impacted since it may not make flush contact with the rod.
Moreover, the use of known counter-torque wrenches permits screws to rotate out of alignment relative to the rod during tightening if the counter-torque wrenches are levered on during the act of tightening. Compressing across screws with a standard counter-torque wrench in place can cause the screw to translate as well as rotate out of proper alignment if force is not applied to the counter-torque wrench to reorient the screw into the proper orientation. The misaligned condition caused by levering on the standard counter-torque wrench may result in a gap between a set screw and the rod. The act of tightening the set screw would need to overcome any forces preventing proper orientation.